This invention relates generally to methods and apparatus for manufacturing composite articles. More particularly, this invention relates to flexible tooling apparatus and methods that utilize an inflatable balloon or bladder for molding articles made of a composite material, especially to conformably molding a second material to a rigid object formed of a first material so as to produce a composite article.
Composite materials are generally used in a wide variety of applications to increase the strength and durability of a part or article of manufacture. Use of composites has been represented extensively in many diverse applications such as aeronautics and sporting equipment. For example, composite materials recently have been investigated to increase the durability of a traditional wooden baseball bat.
The history of using composites in the manufacture of baseball bats is exemplary to the use of composites in general. Until the last 20 years, only solid wood was used to make baseball bats. Over the past few decades, however, numerous amateur leagues have allowed non-wooden bats made from aluminum and composites. While the initial intent of using a non-wooden bat was to increase durability, many non-wooden bats were designed to hit a ball further than otherwise would be accomplished using a solid-wood bat. This increased hitting performance is a cause of concern for some. The increased speed of a batted ball is believed to increase the risk of injury to players, while the increased hitting ability may provide an advantage to the batter, thus changing the traditional balance of defense and offense. These concerns, combined with the upward spiraling costs of some non-wooden bats, have led to renewed interest in wooden bats.
The configuration of a conventional wooden bat and the material properties of wood limit the use of traditional techniques for manufacturing a wood-composite bat. Generally speaking, composite parts are molded using either hard or flexible tooling. During molding, heat and pressure are applied to facilitate the curing of the molded material. When molding a composite layer applied to a wooden bat, however, heat may not be used to reduce cure time because wood has limited temperature resistance and exhibits high moisture expansion. Thus, a molding process for making a composite-reinforced wooden bat must operate at ambient temperatures.
Hard tooling involves the use of molds made of rigid materials. Rigid molds are expensive to fabricate and difficult to modify. A rigid mold also produces undesirable mold lines in the finished part, and generally can be used only with an article having a particular size and shape for which the mold was designed. Because, for example, there are a large number of commercially available bats of varying sizes, flexible tooling is preferable to hard tooling for applying a composite reinforcement material to wooden bats.
Flexible tooling incorporates a flexible mold comprised of an elastomeric material that can stretch and conform to a complex part geometry. Conventional flexible molding operations include xe2x80x9cconsolidation wrappingxe2x80x9d and the use of a xe2x80x9ctube-clavexe2x80x9d device. A tube-clave comprises a rigid pipe having an internal tubular diaphragm connected to the pipe at each end of the pipe, thereby forming a sealed chamber between the diaphragm and the walls of the pipe. The interior cavity of the diaphragm constitutes the tube-clave. A vacuum applied to the chamber (between the diaphragm and the pipe walls) expands the diaphragm radially outward toward the pipe to allow an article (covered with a curable composite material) to be inserted into the tube-clave. Positive pressure is then applied to the chamber, forcing the diaphragm toward the article and providing consolidation of the composite material during cure. After the composite material is cured, a vacuum is re-applied to the chamber to allow the article to be removed from the tube-clave.
In some cases, tube-claves have proven to be unsatisfactory for curing a composite layer applied to the surface of an elongated article. For example, the diaphragm of a tube-clave is unable to adequately conform to the contour of an elongated article such as a bat having a diameter at an end that is substantially larger than the diameter of a middle portion such as the handle. In addition, tube-clave diaphragms have a limited usefuil life and need to be replaced frequently. As a result, a large number of tube-claves is necessary to effectuate an efficient manufacturing process.
In xe2x80x9cconsolidation wrapping,xe2x80x9d heat-shrink tape, strips of release cloth, or other wrapping material is applied to the surface of an article comprising a curable composite material to provide consolidation of the curable material during curing. Although the wrapping material conforms to the contour of an article better than a tube-clave, consolidation wrapping requires a high level of operator skill, and usually requires that the article be sanded or smoothed after removal of the wrapping material.
Therefore, there exists a need for new and improved apparatus and methods for manufacturing any of various articles having a composite material applied to a surface of the article.
In view of the foregoing disadvantages inherent in conventional methods and apparatus used to manufacture composite articles, the present invention provides improved flexible tooling apparatus for molding a sleeve or analogous structure, made of a second material, to the surface of an article made of a first material so as to form a composite article, and molding methods that use such apparatus. The present invention also provides methods and apparatus for producing composite articles with reduced production costs and with a lower level of worker skill, and that optimize properties of the first and second materials by allowing proper curing of the material.
To such ends, and according to one aspect of the invention, an apparatus is provided for molding a unit of a second material onto an article made of a first material. An inflatable, flexible bladder is fluidly connectable to a source of a pressurized fluid, such as compressed air. The pressurized fluid is used to inflate the bladder such that, when the bladder is at least partially inflated with the fluid, the article may be pushed against the bladder to invert the bladder and cause the exterior surface of the bladder to form a flexible mold around at least a portion of the article. Desirably, the bladder is tubular in shape so as to longitudinally and circumferentially conform to the contour of the article during molding.
According to another aspect, a method is provided for molding an article made of composite material. In one specific embodiment, an inflatable, flexible bladder is at least partially inflated with a pressurized fluid. The article is urged against the inflated bladder sufficiently to invert the bladder around at least a portion of the article to form a pressurized mold around a surface of the article to be cured with the inflated portion of the bladder. Movement of the article relative to the bladder is restricted for a time sufficient to permit curing of the article. After completion of curing, the article is separated from the bladder.
According to another embodiment, a method is provided for molding a unit of a first material to the surface of a support structure. First, the first material is applied to the support structure in any conventional manner. A flexible bladder is inflated with a pressurized fluid. The structure is then urged against the inflated bladder sufficiently to invert the bladder around at least a portion of the structure to form a pressurized mold around a surface of the material. Movement of the structure relative to the bladder may be restricted to permit curing of the material in the bladder. After completion of curing, the structure is separated from the bladder and the cured material may be removed from the support structure. Alternatively, the structure may be removed from the bladder before the first material has cured, in which case the pressurized bladder is used to shape the first material to the surface of the support structure.
According to yet another embodiment, a method for molding an article comprising a composite material includes introducing a pressurized fluid into an inflatable bladder. The article is then urged against the bladder so as to invert the bladder substantially around the entire article and cause the bladder to form a pressurized mold around the article. A substantially equalized pressure exerted on the article by the bladder restricts movement of the article relative to the bladder as the composite material on the article cures. After curing is completed, the article is removed from the bladder.
These and other aspects and features of the invention are described below with reference to the accompanying drawings.